Field of the Invention
The invention relates to an amplifier array for high-frequency signals, including a differential amplifier array having at least two transistors with emitters being coupled through a coupling element and base terminals each receiving a signal to be amplified. The invention also relates to a multiplexer configuration having at least one such amplifier array.
In amplifier arrays which have been described heretofore, for instance in the textbook by Tietze and Schenk, entitled: "Halbleiterschaltungstechnik" [Semiconductor Circuitry] 9th edition, 1991, pp. 66-73, differential amplifier stages with or without slight negative resistive feedback of the emitters are used. The input transistors are coupled directly to the input signals.
Those amplifier stages have a disadvantage which is that the amplification is effective over a wide frequency bandwidth. In principle, that bandwidth ranges from the equisignal component to the limit frequency of the amplifier, which is dictated essentially by the parasitic effects of the components. That means that not only the high-frequency useful signal but also low-frequency noise signals in the base band are amplified. Such noise signals can be coupled-in, for instance, as a result of preceding signal processing circuits, logic circuits or leakage pickup. If the amplifier stages are followed by mixers or modulators, then the noise signals in the base band are also superimposed on the useful signal in the carrier band. That is undesirable, since it reduces both the useful-signal-to-noise ratio and the dynamics.